O'Rourke teased his announcement on Wednesday evening, telling MSNBC that he and his wife "have made a decision about how we can best serve our country," adding that "we are excited to share it with everyone soon."

O'Rourke did very well in many polls leading up to his defeat, considering that Texas typically elects Republicans. And in the election, itself, he lost by a very slim margin — securing 48.3 percent of the vote to Cruz's 50.9 percent, according to The New York Times. This led pundits around the country to question how much longer Texas would remain the conservative stronghold it long has been. And, despite his loss, many onlookers characterized his campaign an overall success in light of that.

Given the dense pool of Democratic candidates and the fact that the election is still more than a year and a half away, it's too early to say how O'Rourke will fare on the presidential campaign trail.

"This is a defining moment of truth for this country and for every single one of us," the 46-year-old former Texas congressman said in his video announcement. "The challenges that we face right now, the interconnected crises in our economy, our democracy and our climate have never been greater. And they will either consume us, or they will afford us the greatest opportunity to unleash the genius of the United States of America."

He continued to say, "This moment of peril produces perhaps the greatest moment of promise for this country and for everyone inside it."

O'Rourke promised to run a "positive campaign" that seeks to unite "a very divided country," mentioning the importance immigration, criminal justice reform, and climate change will play in his bid for the White House.

He will hold a campaign kickoff event in El Paso, Texas, on March 30. Even if you can't be in Texas, O'Rourke said he still wants your help organizing where you live for "the greatest grassroots campaign this country has ever seen."